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D. Grassi, V. Formisano (IFSI-CNR, Area di ricerca Roma Tor Vergata)
Most of IRIS Mariner 9 data show strong absorption features due to dust in Martian atmosphere. Averaging thousands spectra an instrumental effect has been identified and studied. Once the data are corrected for the instrumental effect they allow the study of Martian dust composition. Spectra have been classified according main dust band depth, quantified here by a numerical parameter D. Measurements acquired in condition of very low temperature have been eliminated. Data inside each class have been averaged to get a better signal to noise ratio. In order to compute transmittance related to dust, a synthetic spectra for a pure CO2 atmosphere has been computed using the vertical temperature profile obtained by inversion of 15 micron CO2 band in each average spectra. A simple numerical filtering has allowed us to individuate positions of minor bands (inside the main dust absorption feature), with depths are directly correlated to D values and therefore to be ascribed to dust. Locations of maxima and minima are indicative of an high silicon content in the suspended materials, while a direct comparison with transmittance spectra shows a strong similarity with albite, that is proposed here as the main dust component. Another feature around 1650 cm-1 is easily seen in average spectra and can be indicative of sulfate materials. A comparison between the elemental composition of albite (plus sulfate) and the one measured for loose soil at Pathfinder site suggests the following dust composition (in mass): 50 gypsum, 20
The author(s) of this abstract have provided an email address for comments about the abstract: grassi@sunbice.ifsi.rm.cnr.it